-=> Mike Ross said to Greg Mayman
 -=> about "LIGHTNING STRIKE" on 01-04-03  22:26.....

 MR> Sure, HV will get by but the point of the 1488/89 ic's is that they
 MR> have relatively large value resistors in-line with the signal and these
 MR> tend to absorb a lot of grief from whatever is connected to the ic. I

Yup.

 MR> didn't mean the ic would survive indefinetly but if the cleaning lady
 MR> goes by with a vacuum cleaner and induces a nice little static spark
 MR> into the phone line then the 1488/89's series resistors will mitigate
 MR> the damage on a regular basis and none is the wiser.

Hmmm... it just occurred to me that the 1488/89 are on the RS232
lines ONLY.

The stuff that is likely to take the zaps from the phone line is
mainly the IC that does the FSK modulation and demod, between the
UART and the phone line.

With an internal modem there wouldn't be any 1488/89 chips in the
circuit.

 GM> I still prefer an external modem. It puts several more ICs and
 GM> some solid physical separation between the phone line and the
 GM> motherboard ;-)
 MR> Not to mention more grounding opportunities for glitches to jump to.

Correct!

 MR> Yes, I don't see the point either of stealing cpu cycles to run a
 MR> modem. Heck most of the cost of a modem is in the packaging not the
 MR> circuit! 

When you have had to upgrade from your old 33MHz CPU to 600MHz or
faster CPU to run the latest software, there are a lot of CPU
cycles to spare all over the shop.

But AFAIK most of the internal modems use their own internal
processors for the nitty-gritty. The main CPU is doing no more
than it would be with a serial port connected to an external
modem.

From Greg Mayman, in beautiful Adelaide, South Australia

... Be on the level and you're less likely to go downhill.
___ Blue Wave/386 v2.30

--- FLAME v2.0/b